April in the hills with Chris Horne and Barbara Mitcalfe

Cyathea dealbata, ponga, silver fern

Trunk, 'pegs' and fronds of Cyathea dealbata Photo: Jeremy Rolfe

Young Cyathea dealbata fronds Photo: Jeremy Rolfe

You will see ponga, an endemic NZ tree fern species, in lowland to lower montane forest and shrub land, from sea level to 600 m, throughout the North and South islands, and on Chatham Island / Rekohu. As the most drought-tolerant of the Cyathea genus, it favours well-drained sites, so it is not common in the wetter parts of the South Island’s West Coast. The trunk can be up to 10 m tall and about 45 cm diameter at its base. The fronds, dark green above, extend roughly horizontally and are up to 4 m long and 1 m wide. As old fronds die and fall off, they leave behind persistent, prominent, light brown peg-like, stem-bases a little thicker than your thumb. Remember the mnemonic in the March 2014 article: ‘P’ for pegs, ‘P’ for ponga.

Cyathea means ‘cup-like’, referring to the form of the indusium which protects the unripe reproductive parts, called spores, on the underside of the frond. Dealbata means ‘whitish’, referring to the underside of the adult fronds, the basis of one of New Zealand’s best known emblems. Young ponga fronds lack the white underside.

The name ‘ponga’ is often mispronounced as ‘punga’, and that word is applied indiscriminately and incorrectly to all of our seven species of tree fern. Please avoid it because it is both wrong and confusing.

Look for the spiral coils of young fronds – koru – covered with brown hairs and scales, and also the white stalks of the mature fronds. Growing on the trunk, among the frond stumps, you will often see seedlings of trees such as kāmahi and five-finger and many species of ferns which have germinated on the trunks.

Use

Māori used to spread the fronds on sleeping places in their whare. They used the poisonous, fibrous, woody part of the trunk as tips for some of their weapons. Ponga pith had many rongoa uses - it was used to make poultices, and taken internally, the gum was used to expel worms. Early European settlers in Southland built huts called ‘bungi huts’ with ponga walls. In some native forests, tree fern trunks are used to form “corduroy tracks”.